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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 15 June

Astrophysics of Galaxies

A Strong Stellar Age-Metallicity Gradient Relation in Nearby Dwarf Galaxies Driven by Stellar Migration and Environmental Quenching

Tie Li, Hong-Xin Zhang, Wenhe Lyu et al. (+16 more)

Stellar metallicity gradients ($\nabla[Z/H]$) provide a fossil record of the assembly history of galaxies. We present an analysis of $\nabla[Z/H]$ for 90 nearby low-mass galaxies using VLT/MUSE IFU spectroscopy, spanning stellar masses from $10^{6.5}$ to $10^{10} M_\odot$ (median $\sim 10^{8.5} M_\odot$) and significantly extending the mass coverage of existing IFU surveys into the classical dwarf regime. Our primary finding is a robust negative correlation between $\nabla[Z/H]$ and light-weighted stellar age ($|r|\gtrsim 0.7$) measured out to $\sim$ 2$\times$ effective radius: older dwarf galaxies have steeper (more negative) gradients. This holds regardless of stellar mass, structural compactness, or large-scale environment (group/field), and is strongest in the intermediate-mass regime ($8.2\lesssim\log M_\star/M_\odot\lesssim9.0$). The slope of the age-$\nabla[Z/H]$ relation is close to that in the FIRE-2 simulations, indicating that stellar radial migration driven by feedback-induced potential fluctuations may be fundamental in dwarf evolution. But this apparent consistency is likely coincidental given the simulations' overly efficient feedback and chemical mixing. On the other hand, the H\,i deficiency parameter, an indicator of past environmental stripping, shows a moderate yet highly significant correlation with $\nabla[Z/H]$, second only to stellar age in strength: galaxies with higher H\,i deficiency tend to have more negative gradients, strongly indicating that environment-driven outside-in quenching and the ensuing gradual truncation of metal enrichment re-shape the stellar metallicity distribution. Our analysis suggests that the chemical evolution of dwarf galaxies likely arises from a synergy of feedback-driven dynamical heating and external environmental processing, though only the latter has robust observational support.
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All authors Tie Li, Hong-Xin Zhang, Wenhe Lyu, Weibin Sun, Bojun Tao, Weiyu Ding, Xu Kong, Guangwen Chen, Jianhui Lian, Yong Shi, Fuyan Bian, Xin Li, Xiaoling Yu, Zhiyuan Zheng, Yanmei Chen, Qiusheng Gu, Junfeng Wang, Shude Mao, Kai Zhu

Astrophysics of Galaxies

The Rapid ASKAP Continuum Survey (RACS) VIII: total intensity and circular polarization images and catalogues at 887.5 MHz from RACS-low2

S. W. Duchesne, K. Rose, Tara Murphy et al. (+9 more)

We present a new data release from the Rapid ASKAP Continuum Survey (RACS), a widefield snapshot radio survey conducted with the Australian SKA Pathfinder (ASKAP). This data release contains the second RACS epoch to make use of ASKAP's low-frequency band, centred on 887.5 MHz with a bandwidth of 288 MHz, referred to as RACS-low2. This RACS-low2 data release includes both Stokes I and V imaging and catalogue data products covering the whole sky up to a declination of ~+48 degrees. RACS-low2 largely follows the observation footprint of the first low-band epoch, though includes additional coverage in the Northern Hemisphere. The observation scheduling and data processing follow previous RACS epochs, making use of autonomous scheduling and holography-derived primary beam models. The Stokes I and V catalogues are derived from images with a median point-spread function (PSF) of 14.2" times 11.8", and have median root-mean-square noise properties of 195 and 163 micro-Jy/PSF, for the Stokes I and V images, respectively. The consolidated Stokes I catalogue contains 3922151 sources. We also constructed a catalogue of Stokes V sources by measuring Stokes V images at the Stokes I source positions. For the 221 Stokes V measurements above the estimated leakage and detection thresholds we provide likely identifications, including detections of 61 radio stars, 85 pulsars, 43 AGN (many likely to be residual leakage), and one source that is not associated with a known astronomical object. These data products, including calibrated visibilities, images, source lists, and consolidated catalogues, are made publicly available through the CSIRO ASKAP Science Data Archive (CASDA).
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All authors S. W. Duchesne, K. Rose, Tara Murphy, Laura N. Driessen, Joshua Pritchard, V. A. Moss, T. J. Galvin, E. Lenc, A. W. Hotan, K. Ross, A. J. M. Thomson, Matthew T. Whiting

Cosmology and Nongalactic Astrophysics

Neutrino Constraints on memory-burdened Primordial Black Holes from Dwarf Spheroidal Galaxies

Xiu-Hui Tan, Jun-qing Xia and Yu-Feng Zhou

Dwarf spheroidal galaxies (dSphs) represent prime targets for indirect dark matter (DM) searches due to their substantial DM content and low astrophysical backgrounds. In this work, we conduct a comprehensive search for neutrino signals originating from memory-burdened primordial black holes (PBHs) as DM candidates, utilizing 10 years of publicly available muon-track data from the IceCube Neutrino Observatory. We systematically compile $\mathcal{D}$-factor measurements from four independent literature sources, resulting in a robust sample of 14 dSphs with well-characterized DM distributions. For each dSph, we perform an unbinned maximum-likelihood analysis to evaluate the significance of potential PBH neutrino emission, incorporating $\mathcal{D}$-factor uncertainties through a profile likelihood framework. No significant excess over the background-only hypothesis is detected. Building upon these null results, we derive upper limits on the PBH abundance fraction, assuming a monochromatic mass distribution. Our analysis demonstrates that constraints obtained in the $k=1$ case exhibit significant improvement compared to previous studies, while the $k=2$ case yields less restrictive limits due to limited sensitivity of IceCube in the relevant energy range. Furthermore, our combined analysis of 14 dSphs achieves substantially enhanced sensitivity, as the independent error treatment effectively reduces statistical uncertainties.
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Earth and Planetary Astrophysics · Cross-listed from physics.space-ph

Direct Observations of Magnetic Reconnection in the Solar Wind Current Sheets near Mars

Chi Zhang, Chuanfei Dong, Xinmin Li et al. (+10 more)

Magnetic reconnection is a fundamental and ubiquitous process in astrophysical plasmas that converts magnetic energy into plasma kinetic and thermal energy. Throughout the heliosphere, the solar wind is permeated with current sheets (CSs), providing a natural laboratory for investigating this process. Using measurements from NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we report the first direct observations of magnetic reconnection occurring within the solar wind CSs near Mars. Specifically, MAVEN observed the classic Petschek-type reconnection exhaust regions, evidenced by bifurcated magnetic field signatures and Alfvenic ion outflows. Notably, the observed exhaust region appears to be large-scale, significantly exceeding the typical thickness of solar wind CSs near Mars. This suggests that magnetic reconnection may significantly broaden the CS. Our results underscore the ubiquity of magnetic reconnection across heliocentric distances and may provide new insights into the large-scale evolution of the solar wind and the development of turbulence within it.
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All authors Chi Zhang, Chuanfei Dong, Xinmin Li, Han-Wen Shen, Jasper Halekas, Tai Phan, Christian Mazelle, Yuki Harada, Hongyang Zhou, Jiawei Gao, Liang Wang, Shannon Curry, David L. Mitchell

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

LIGO, LISA and Ultralight Axion-like Dark Matter

Lawrence M. Krauss

A coherent cosmic background of axion-like particles (ALPs) coupled to photons can produce a small periodic differential phase or polarization modulation for photons traversing separate arms in gravitational wave interferometers, peaked at a frequency associated with the particle mass, and suppressed whenever the dark-matter coherence length $\lambda_{\rm coh}$ exceeds the arm length~$L$. For the LIGO audio frequency band the sensitivity to cosmic ALPs is below current bounds. For LISA, however, the natural mass range $m_a \sim 4\times10^{-19}$–$4\times10^{-16}$~eV – corresponding to a sideband frequency in LISA's science band of $0.1$~mHz–$0.1$~Hz – may be observable. A 1-year shot-noise-limited search projects a sensitivity $g_{a\gamma\gamma} \lesssim 5\times 10^{-14}$~GeV$^{-1}$ across most of the band, reaching $\sim 7\times 10^{-15}$~GeV$^{-1}$ near $0.1$~Hz, which is $10^{3}$–$10^{4}$ below the CAST helioscope bound. An RF heterodyne photodetection upgrade – to either detector – might extend the search sensitivity to $g_{a\gamma\gamma}\sim 6.5\times 10^{-14}$~GeV$^{-1}$ at $m_a\sim 3\times 10^{-7}$~eV for LIGO and $g_{a\gamma\gamma}\sim 3.3\times 10^{-17}$~GeV$^{-1}$ at $m_a\sim 5\times 10^{-13}$~eV for LISA. Dark-matter substructure can affect the signal in a several interesting ways.
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Solar and Stellar Astrophysics

Vector Magnetic Field associated with an Active Region Filament Observed by SUNRISE III/SCIP in the Ca II 8542 Å Line

Takuma Matsumoto, Yukio Katsukawa, Masahito Kubo et al. (+38 more)

We report high-spatial-resolution spectropolarimetric observations spatially associated with a solar filament, obtained with the SUNRISE Chromospheric Infrared spectro-Polarimeter (SCIP) onboard the SUNRISE III balloon-borne solar observatory on 15 July 2024. The observed filament was located near the solar disk center, adjacent to an active region, and remained quiescent for at least two hours during the observing period. SCIP recorded full Stokes profiles in the Ca II 8542 Å line, revealing clear signatures of linear polarization produced by the transverse Zeeman effect. The detected linear polarization signals within the filament region exceeded the 2$\sigma$ noise level and exhibited a characteristic Zeeman double-lobe spectral shape that distinguishes them from polarization due to scattering. The magnetic field strength derived using the weak field approximation is approximately -80 G along the line of sight and 300-500 G in the transverse direction. These values likely reflect the magnetic properties of the filament and its supporting chromospheric environment. The orientation of the magnetic field vector is nearly parallel to the filament axis in its northeastern portion, while the southeastern part of the filament extends outside the field of view. To our knowledge, this is the first unambiguous detection of linear polarization associated with a solar filament with the Ca II 8542 Å line. Our results open a new diagnostic window on the vector magnetic structure of solar filaments in the lower chromosphere, complementing existing He I based diagnostics that probe the upper chromosphere.
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All authors Takuma Matsumoto, Yukio Katsukawa, Masahito Kubo, Yusuke Kawabata, Takayoshi Oba, Ryohtaroh T. Ishikawa, Yoshihiro Naito, Hirohisa Hara, Toshifumi Shimizu, Fumihiro Uraguchi, Toshihiro Tsuduki, Kazuya Shinoda, Tomonori Tamura, Yoshinori Suematsu, Carlos Quintero Noda, Sami K. Solanki, Andreas Lagg, Achim Gandorfer, Jose Carlos Del Toro Iniesta, Pietro Bernasconi, Thomas Berkefeld, Alex Feller, Tino L. Riethmüller, Alberto Álvarez-Herrero, H. N. Smitha, David Orozco Suárez, Bianca Grauf, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Julian Blanco Rodríguez, Juan Sebastián Castellanos Durán, Edvarda Harnes, Johannes Hölken, Francisco A. Iglesias, Azaymi L. Siu Tapia, Hanna Strecker, Dušan Vukadinović, Pablo Santamarina Guerrero, Nour E. Raouafi

Astrophysics of Galaxies

The Dynamics of Old Inner Galaxy Stars in Milky Way-mass Galaxies Using FIRE-2 Simulations

Emma Tasso, Madeline Lucey, Robyn Sanderson et al. (+2 more)

Understanding how galaxies like the Milky Way assembled over cosmic time remains a central question in astrophysics. Understanding the processes that shaped their formation and evolution is greatly enhanced by the joint use of observational data and high-resolution cosmological simulations. Old stars in the inner regions of galaxies serve as powerful tracers of early dynamical events, having formed during the initial stages of galaxy assembly and retaining the kinematic imprints of those formative periods. We investigate the kinematic properties of old (age $>10$ Gyr) inner galaxy ($r_\mathrm{GC}<5$ kpc) stars in thirteen Milky Way-mass galaxies from the FIRE-2 cosmological zoom-in simulations, focusing on their origin, orbital structure, and kinematic alignment with the disk. Our analysis reveals that old stars in the inner galaxy are more likely to have been formed in their host galaxy, although accretion is seen most prominently during the earliest stages of galaxy formation. Many of these accreted stars tend to occupy kinematically hot orbits compared to their counterparts formed in the host galaxy, although some stars formed in-galaxy also retain kinematically hot orbits. Disk-like dynamics are present throughout all age bins, and are most prominent as age decreases. Although some old stellar populations retain disk-like structure, the prominence of this rotational component varies significantly across galaxies and between star populations. These results emphasize the diversity of early galaxy assembly histories and suggest that coherent angular momentum in accreted material can leave detectable kinematic signatures in present-day stellar halos.
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All authors Emma Tasso, Madeline Lucey, Robyn Sanderson, Aritra Kundu, Lina Necib

Sunday 14 June

Solar and Stellar Astrophysics · Cross-listed from physics.pop-ph

The Optics of Shadow Bands

Branko Sretenović

Shadow bands are transient, rippling patterns of light and dark that may appear in moments before and after totality in a solar eclipse. Despite centuries of reports, their physical origin has remained unresolved. This preprint develops a geometric-optical solution in which the Sun's extended structure produces a celestial analogue of Young's double-slit experiment, generating an interference-like intensity pattern on the ground, modulated by Earth-atmosphere effects. The analysis combines solar limb geometry, atmospheric propagation effects, and a wave-based formulation that yields quantitative predictions for fringe width and spacing. The resulting model accounts for the principal observational features of shadow bands and clarifies why the phenomenon is both elusive and highly sensitive to viewing conditions.
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2606.28366 · 14 Jun · Version 2: Minor formatting update (font size, references). Scientific content unchanged. This preprint is accompanied by supplementary materials available at Zenodo: https://doi.org/10.5281/zenodo.20561234 . A supplementary and pedagogical exposition of this framework appears in the author's book The Optics of Shadow Bands (2025)

Abstract PDF $SOLAR ×2$GEOM ×1

Instrumentation and Methods for Astrophysics · Cross-listed from physics.pop-ph

Mass Extinctions by Gravitational Tides

Daniele Fargion

Past and recent observations suggest that many planetary mass or dwarf planet objects may exist in the outer Solar System. Gravitational perturbations may occasionally bring some of them into the inner Solar System. The early, rare collision between the early Earth and a Mars sized body is generally invoked to explain the formation of the Moon. More probable than a direct impact, are grazing or near Earth flybys of similar objects. Such passages may have left strong tidal signatures: giant waves, large volcanic episodes, sea regressions, coherent meteor showers, and major climatic perturbations. These mechanisms could have contributed to several major biological mass extinctions over the past $600$ million years, as suggested by peculiar correlations in the geological record. Similar events may have occurred several times during the earlier history of Earth. Accretion of mini planets by largest planets and in particular by the Sun may also have occurred many more times over the last four billion years. Possibly producing additional temperature variations on planets and Earth.
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High Energy Astrophysical Phenomena

Misspecification in amortized X-ray spectral inference: a detection benchmark, a gain shift three schemes cannot see, and marginalizing it out

Karan Akbari

Amortized neural posterior estimation fits X-ray spectra in milliseconds, and pipeline use will lean on post-hoc checks to catch detector systematics the simulator misses. We measure what those checks see, on simulated spectra from real XMM-Newton EPIC-pn and NICER responses. Of four misspecification families, an unmodelled 6.4 keV line and partial covering are catchable per spectrum (AUC 0.97 and 0.84). A wrong continuum family reaches 0.66. One flow passed every recovery check yet under-covered (coverage deviation 0.114), and a converged NICER flow (0.011) fails simulation-based calibration on all five parameters. Recovery metrics do not certify calibration. Three schemes catch the line: the posterior-predictive check, importance sampling against the exact Poisson likelihood (effective sample size, 0.68-0.82), and the nested-sampling evidence (count-controlled, $-67$ to $-892$ nats). None catches the 3 per cent gain shift, 2.4 to 14.4 times the EPIC-pn energy-scale accuracy (AUC 0.44-0.54; 36-cell means 0.50 and 0.49 on both responses; paired evidence $+0.33 \pm 1.37$ nats). The effective sample size stays null-consistent from 0.1 to 10 per cent, realistic amplitudes included. The shift still biases the photon index by $+0.02$ (0.03 to 0.11$\sigma$) at both count levels. Retraining with a per-simulation nuisance gain adds no inference-time cost, and the gain posterior returns the prior. The bias survives, and exact gain-marginalized nested sampling shows the flow capturing at most 0.163 of its gain constraint (continuous-prior convention) at high counts. Marginalization over posited calibration nuisances is the working defence for X-ray SBI at catalog scale; no check we ran supplies a warning.
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2606.17098 · 14 Jun · 14 pages, 6 figures, 4 tables. v4: substantially extended, new title; adds an importance-sampling scheme, a cross-scheme detectability matrix with measured nested-sampling errors, and a gain-marginalized retraining fix cross-checked against exact nested sampling. Code and data: https://github.com/WizardEternal/sbi-xray-calibration

Abstract PDF $BNCH ×1$CELL ×1$PHOT ×1

Astrophysics of Galaxies

HYPERION. The cold ISM of rapidly growing $z>6$ quasars: diverse gas reservoirs, dust enrichment, and feedback signatures

Claudia Maria Pierro, Roberta Tripodi, Laura Pentericci et al. (+11 more)

Luminous QSOs at $z>6$ host some of the most rapidly assembled SMBHs in the early Universe. Characterizing their cold ISM is essential to determine their evolution. We investigate the molecular gas, cold dust, star formation, gas-to-dust ratio, and ionized ISM of ten HYPERION QSOs using new ALMA Band 3 observations targeting CO(6-5) and the underlying $\sim100$ GHz continuum, complemented by archival and literature ALMA/NOEMA data. We detect $\sim100$ GHz continuum emission in eight targets and CO(6-5) emission in four QSO hosts, J025-33, J083+11, J231-20, and J0252-0503, as well as in the companion of J231-20. The inferred molecular gas masses are of order $10^{10}~M_\odot$, while the non-detections imply upper limits of a few $10^9~M_\odot$, indicating a broad range of molecular reservoirs within the HYPERION population. For J025-33 and J083+11, the FIR SEDs are well sampled and yield low dust temperatures, $T_{\rm dust}=36^{+13}_{-7}$ K and $32^{+4}_{-3}$ K, respectively, well below the average value for $z>6$ QSOs. Combining gas and dust masses, we find a gas-to-dust ratio for J083+11, ${\rm GDR}=16^{+5}_{-4}$, among the lowest measured in a high-redshift QSO host. We also detect [NII]$\lambda 205\,\mu$m emission in J025-33 and tentatively in J083+11, suggesting dense or highly structured ionized gas. Finally, we identify a tentative connection among $T_{\rm dust}$, the X-ray photon index $\Gamma$, and the C IV velocity shift. These trends may indicate that more powerful winds redistribute dust away from the central AGN heating source, lowering its temperature and weakening the connection between the large-scale dust reservoir and the X-ray corona. Overall, HYPERION QSOs emerge as a heterogeneous population in which SMBH growth, star formation, gas consumption, enrichment, and feedback are not necessarily synchronized.
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All authors Claudia Maria Pierro, Roberta Tripodi, Laura Pentericci, Francesco Salvestrini, Luca Zappacosta, Alessia Tortosa, Blessing Musiimenta, Enrico Piconcelli, Livia Vallini, Fabio Di Mascia, Federico Esposito, Chiara Feruglio, Fabio Vito, Maria Vittoria Zanchettin

Cosmology and Nongalactic Astrophysics

Axion-Sourced Gravitational Waves in $\mathrm{B\!-\!L}$ Hybrid Inflation

Ahmed Ayad and Shaaban Khalil

Minimal supersymmetric $\mathrm{B\!-\!L}$ hybrid inflation predicts a negligible vacuum tensor-to-scalar ratio $r_{\rm vac}\sim 10^{-8}$ due to its extremely flat potential. In this letter, we show that adding a spectator pseudoscalar axion-like field coupled to the $\rm {U}(1)_{\mathrm{B\!-\!L}}$ gauge sector via a Chern-Simons term circumvents this suppression. The rolling axion triggers a tachyonic instability for one gauge field helicity, exponentially amplifying gauge fluctuations. These sourced modes generate a stochastic gravitational-wave background with tensor power spectrum ${\cal P}_{T}^{\rm src}\propto e^{4\pi\xi}/\xi^{6}$, where $\xi = \alpha \dot{\phi} / (2 f_a H)$ is the gauge-field instability parameter. For $\xi\sim3.3$–$3.6$, the tensor-to-scalar ratio reaches $r\sim10^{-3}$, within the sensitivity of LiteBIRD. For $\xi\sim3.6$, the gravitational-wave spectrum develops a peaked shape that enters the LISA sensitivity band (peaking at frequencies around $10^{-3}$ Hz) with an amplitude $h^2\Omega_{\rm GW}\sim2.5\times10^{-13}$. The mechanism predicts chiral gravitational waves, a broken consistency relation $r=16\epsilon$, and a distinctive $r$–$\Omega_{\rm GW}$ correlation that could be tested by future CMB and interferometer observations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Axiverse Strings Resolved

Rudin Petrossian-Byrne and Giovanni Villadoro

Axiverse cosmic strings are resolved by non-perturbative string states with large tension. We show how, in some regions of moduli space, they dissolve into low-tension configurations that are fully captured by field-theoretic solitonic solutions, such as 't Hooft-Polyakov-like strings, allowing a post-inflationary cosmology within the original axiverse paradigm.
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Earth and Planetary Astrophysics

The breaking of cold traps and onset of titanium in ultra-hot Jupiter atmospheres: WASP-189b in context

Stefan Pelletier, Romain Allart, Valentina Vaulato et al. (+56 more)

Condensates are ubiquitous to all Solar System planets with significant ($>$10mbar) atmospheres. The same is true for most exoplanets with characterised atmospheres, with even ultra-hot exoplanets being able to form clouds on their cooler nightsides. One high-interest condensate is titanium, a highly refractory element that as an oxide (TiO) is a potent optical absorber long believed to be a driver of thermal inversions in highly irradiated exoplanet atmospheres. Observations have shown that some ultra-hot Jupiters have strong thermal inversions despite being significantly Ti-depleted, likely due to cold trapping, raising doubts about whether TiO is the main cause of their inverted temperature structures. Our aim was to retrieve the titanium-to-iron ratio of the dayside atmosphere of the ultra-hot Jupiter WASP-189b to determine whether the full titanium budget is accounted for in the gas phase. We analysed thermal emission observations of WASP-189b taken with the HARPS and NIRPS spectrographs using different atmospheric retrieval prescriptions to infer the planet's atmospheric thermal structure and composition. We observed Fe and Ti signals in cross-correlation and measured a sub-solar Ti/Fe ratio for WASP-189b using both free and chemical equilibrium retrieval approaches. We find the Ti/Fe of the planetary atmosphere to be between 28% and 81% (1-$\sigma$ bounds) that of the stellar value. The slight underabundance of Ti with respect to Fe on the dayside atmosphere of WASP-189b suggests that some titanium is missing from the gas phase, potentially due to a partial nightside cold trap. In the context of the ultra-hot Jupiter population, the onset of titanium in exoplanetary atmospheres appears to occur progressively, coinciding not with when thermal inversions begin but rather when the vapourisation threshold of titanium is reached on the nightside.
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All authors Stefan Pelletier, Romain Allart, Valentina Vaulato, David Ehrenreich, Eduardo Cristo, Laurie Dauplaise, Christophe Lovis, Leslie Moranta, Nicolas B. Cowan, Thierry Forveille, Étienne Artigau, Frédérique Baron, Susana C. C. Barros, Björn Benneke, Xavier Bonfils, François Bouchy, Marta Bryan, Bruno L. Canto Martins, Ryan Cloutier, Neil J. Cook, Jose Renan De Medeiros, Xavier Delfosse, René Doyon, Jonay I. González Hernández, David Lafrenière, Izan de Castro Leão, Lison Malo, Claudio Melo, Lucile Mignon, Christoph Mordasini, Francesco Pepe, Rafael Rebolo, Jason Rowe, Nuno C. Santos, Damien Ségransan, Alejandro Suárez Mascareño, Stéphane Udry, Diana Valencia, Gregg Wade, Charles Cadieux, Lisa Dang, Emily Deibert, Xavier Dumusque, Dasaev O. Fontinele, Yolanda G. C. Frensch, Frédéric Genest, Roseane de Lima Gomes, Nicole Gromek, Melissa J. Hobson, Vigneshwaran Krishnamurthy, Khaled Al Moulla, Ares Osborn, Caroline Piaulet-Ghorayeb, Bennett Neil Skinner, Avidaan Srivastava, Atanas K. Stefanov, Joost P. Wardenier, Drew Weisserman, Vincent Yariv

Solar and Stellar Astrophysics

Revisiting Approaches to Stellar White-Light Flare Energy Based on Spatiotemporally Resolved Solar Observations

Yingjie Cai, Yijun Hou, Ting Li et al. (+5 more)

Accurately estimating the bolometric energy of solar and stellar white-light flares (WLFs) is crucial for understanding their physical nature and impact on surrounding planets. However, the lack of spatial resolution in stellar observations forced pioneering stellar WLF studies to adopt simplified energy estimation methods, typically assuming either a constant flare temperature or a fixed radiating area. To assess the physical plausibility of these assumptions, we utilize high-spatiotemporal-resolution solar observations to analyze the true evolution of source region's radiating area and temperature of 70 solar WLFs. It is revealed that both area and temperature of most solar WLFs undergo significant temporal evolution, and the flare area strongly correlates with the flare's peak optical continuum flux. Therefore, we propose a new energy estimation method that permits both flare area and temperature to evolve. Compared with existing methods, our dynamic approach yields systematically lower flare energies, which then prompts us to revisit classical macroscopic scaling laws related to the flare energy. It is further revealed that different energy estimation approaches can systematically alter these scaling relations, calling for a re-examination of these established statistical results and their targeted testing or revision in future work.
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All authors Yingjie Cai, Yijun Hou, Ting Li, Ying Li, Mingde Ding, Dechao Song, Changwen Zeng, Jifeng Liu

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Towards the Detection of Thermal Solar Neutrinos

Carlos A. Argüelles, Christopher V. Cappiello, P. S. Bhupal Dev et al. (+3 more)

We show that $\sim$keV thermal solar neutrinos, arising from electroweak processes in the solar plasma, are kinematically accessible to large-volume dark matter direct detection experiments via electron ionization signatures. Using S2-only data from the XENONnT experiment, we place an upper limit on the thermal solar neutrino flux of $\eta \lesssim 1.2 \times 10^8$ times the standard model predicted value, while paired searches from XENONnT, LZ and PandaX give slightly weaker limits. The future XLZD experiment could improve these limits by orders of magnitude. While still far from a detection, this result establishes low-threshold direct detection experiments as a viable probe of the lowest-energy neutrino sources in astrophysics, with important implications for stellar physics and beyond.
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All authors Carlos A. Argüelles, Christopher V. Cappiello, P. S. Bhupal Dev, Pablo Figueroa, Gonzalo Herrera, Icarus Scoville

Astrophysics of Galaxies

Joint Modeling of GD-1 and C-19 as Old Streams

Raymond G. Carlberg, Ting S. Li, Emma Jarvis et al. (+39 more)

DESI observational data for the GD-1 and C-19 streams are compared to stream simulations in an evolving multi-halo potential of a Milky Way-like galaxy based on a cosmological Milky Way-like simulation. The number of subhalos decreases with time and the subhalo-stream encounter velocities rise as the Galaxy and its disk build up their mass. The streams develop from star clusters inserted at $\simeq$1 Gyr after the Big Bang and evolved for 13 Gyr to their current orbital positions. The measured velocity widths of the streams are compared to the matched simulations. Streams in a CDM subhalo population provide the best match to the velocity width, on the average, with considerable scatter. Streams younger than $\simeq$12 Gyr in CDM subhalos are insufficiently hot. Streams in the same potentials but with populations of WDM 5.5 keV subhalos are not, on the average, heated to the observed velocity widths, although some of the realizations do reach the observed levels. The stream density power spectrum measured along the length of the DESI GD-1 sample agrees with the CDM stream simulations, with 1.3 to 2.3 times more power than WDM 7 keV and 5.5 keV simulations. The simulations show that modeling specific streams from the time of the formation of their progenitor clusters is both feasible and necessary to reproduce their stream averaged kinematic properties.
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All authors Raymond G. Carlberg, Ting S. Li, Emma Jarvis, Nasser Mohammed, Joan Najita, Arjun Dey, Sergey E. Koposov, Jakob Piafsky, Leandro Beraldo e Silva, Constance M. Rockosi, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, A. de la Macorra, Biprateep Dey, P. Doel, A. Font-Ribera, J. E. Forero-Romero, Satya Gontcho A Gontcho, G. Gutierrez, R. Joyce, S. Junea, A. Kremin, O. Lahav, M. Landriau, L. Le Guillou, A. Meisner, R. Miquel, W. J. Percival, C. Poppett, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, J. Silber, G. Tarlé, B.A. Weaver, R. Zhou, H. Zou

Cosmology and Nongalactic Astrophysics

Multi-band cross-correlation dark sirens: enhancing cosmological parameter and gravitational-wave bias constraints

Ji-Yu Song, Ya-Nan Du, Yue-Yan Dong et al. (+2 more)

Multi-band gravitational-wave (GW) observation, combining space-borne and ground-based detectors across different frequency bands, can improve the sky localization of compact binary sources by two to three orders of magnitude compared to single-band detection. This enhancement is crucial for cross-correlation dark siren analyses, since the sky localization uncertainty directly determines the noise level of the GW angular power spectrum. In this work, we present the first Fisher forecast for cross-correlation dark siren cosmology with multi-band GW observations, cross-correlating GW events from the Einstein Telescope (ET), Cosmic Explorer (CE), and B-DECIGO with the Chinese Space-station Survey Telescope photometric galaxy survey. We compare three network configurations: the multi-band B-DECIGO+ET+2CE (BDET2CE), the ground-only ET+2CE (ET2CE), and B-DECIGO alone. In the $\Lambda$CDM model, BDET2CE achieves $\sigma(h)/h = 0.35\%$, improving by $37\%$ over the ground-only ET2CE ($0.55\%$) and by $86\%$ over B-DECIGO alone ($2.45\%$). Extending to the $w_0w_a$CDM framework, the multi-band advantage on cosmological parameters becomes more moderate, with BDET2CE improving $\sigma(h)/h$ by $\sim 4\%$ over ET2CE and $\sim 22\%$ over B-DECIGO. The most striking advantage of multi-band observation lies in the per-bin measurement of the GW clustering bias $b_{\rm GW}(z)$: at $z \sim 1-2$, BDET2CE constrains the bias to $\sim 3\%$ precision, compared to $\sim 8-60\%$ for ET2CE and $\sim 20-33\%$ for B-DECIGO. These precise, redshift-resolved bias measurements open a new avenue for probing the astrophysics of compact binary mergers, enabling constraints on formation channels such as isolated binary evolution and dynamical assembly that predict distinct clustering signatures.
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All authors Ji-Yu Song, Ya-Nan Du, Yue-Yan Dong, Jing-Fei Zhang, Xin Zhang

Instrumentation and Methods for Astrophysics

Shigatse Astronomical Site Testing. I. Cloud-cover Climatology and Selected Local Meteorological Conditions

Baiyu Zhang, Hejun Yang, Xiaojun Dong et al. (+15 more)

As the first paper in a Shigatse astronomical site-testing series, we present a multi-source assessment of cloud cover and selected local meteorological conditions at the Shigatse 40 m site on the southern Tibetan Plateau. The study combines CALIPSO-GOCCP active-lidar climatology, ISCCP HXG passive-satellite cloud fields, conventional total-cloud-amount observations from the Shigatse Meteorological Station, and on-site Weather Station measurements. Together, these records characterize Shigatse as a southern-plateau monsoon-transition cloud regime: the active-lidar climatology gives a moderate-to-low annual cloud fraction, and the cloudier months are concentrated in the June–September monsoon interval. In GOCCP, the annual mean cloud fraction is 42.1%, while the October–May low-cloud season has a mean cloud fraction of 26.3%, compared with 73.7% during the June–September monsoon interval. ISCCP gives higher absolute cloud fractions but supports the same seasonal phase and local spatial placement. The aligned 1988–2013 meteorological-station record gives a total-cloud-amount <=40% fraction of 80.7% during October–May, rising to 90.7% in the November–January core, and decreasing to 39.9% during June–September. The 2024–2025 Weather Station archive further shows high fractions of valid samples satisfying the adopted meteorological criteria during the low-cloud months: 92.6% for the October–May night-time proxy and 94.6% for the corresponding 24 h samples. These results identify Shigatse as a measured lower-latitude southern-plateau cloud-cover reference within China's site-testing network, with a well-defined October–May low-cloud observing period and a Shigatse–Ali low-cloud corridor for subsequent regional site testing.
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All authors Baiyu Zhang, Hejun Yang, Xiaojun Dong, Lingling Wang, Juean Luobu, Minfeng Gu, Xiyan Peng, Hao Luo, Yindun Mao, ZhaoXiang Qi, Basangzeren, Qihang He, Guojie Feng, Chunhai Bai, Ali Esamdin, Wenbo Gu, Siqi Wang, Zihuang Cao

High Energy Astrophysical Phenomena

A Universal Physics Defining the Radiation Spectra of Blazars and Gamma-Ray Bursts

Z. Lucas Uhm, Sang-Sung Lee, Bing Zhang et al. (+5 more)

Blazars and gamma-ray bursts (GRBs) are both cosmic beacons of extreme energy release powered by relativistic jets. However, they originate from tremendously different environments. Blazars are the sustained powerhouses driven by supermassive black holes at galactic centers, whereas GRBs are the transient death signals of massive stars or merging compact objects. Here we show that, despite the enormous differences, a universal physics defines the radiation spectra of blazars and GRBs. The blazar spectrum is well described by a "log-parabola" function. Employing a simple toy model with a single optically-thin region of a decreasing magnetic field, we produce the log-parabola spectrum very naturally for blazars. We find that the blazar spectrum is shaped by the "cooling physics" of relativistic electrons in the fast-cooling regime, which we identify as the universal physics since we previously showed that the fast-cooling physics of electrons with a decreasing magnetic field also explains the mysterious low-energy spectral index of the gamma-ray spectrum for a majority of GRBs. This fast-cooling physics of electrons likely nails down the physical origin underlying the universal scaling of the jet energetics between blazars and GRBs, which was observationally suggested more than a decade ago. We highlight that the spectrum shaper in both blazars and GRBs is the cooling physics, not the acceleration mechanism. This finding is conventional-belief-defying and may open up new avenues in a wide range of astrophysics.
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All authors Z. Lucas Uhm, Sang-Sung Lee, Bing Zhang, Judith Racusin, Bindu Rani, Myungshin Im, Aeree Chung, Hyung Mok Lee

Instrumentation and Methods for Astrophysics

Transfer learning for transient search with small-field optical survey telescopes

Kumar Pranshu, Kuntal Misra, Rithesh A et al. (+2 more)

The advent of optical sky surveys has enabled several automated programs for searching transients. Many of these programs extensively use supervised machine learning (ML) algorithms to automate these searches. Effective implementation of such a strategy has an advantage over non-automated methods of transient search in terms of reduced manual labour and reporting latency. Training the relevant ML algorithms often requires extensive labelled training datasets that might not be readily available for new or small field-of-view survey telescopes. Transfer Learning (TL) is an ML technique that is often employed to address this issue by transferring knowledge from a pre-trained model, trained on an extensive dataset for a related task, to enhance performance on a new task with a limited dataset available. This paper demonstrates TL for a Convolutional Neural Network (CNN)-based real/bogus classifier model for transient detection between extensive publicly available image data from the Zwicky Transient Facility (ZTF) and a small and labelled dataset from the 4-m International Liquid Mirror Telescope (ILMT). The same technique was employed to train two different types of transient alert classifiers to characterise the detected candidates based on detection image stamps into 3 and 4 classes, respectively. The resulting model for the real/bogus classifier achieved an accuracy of 97.3% on the test dataset. Additionally, an accuracy of 92.9% was achieved for the 3-class classifier and 85.6% for the 4-class classifier. Furthermore, the statistical significance of the effectiveness of this technique was established with an unpaired t-test between TL models and baseline models trained without TL.
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All authors Kumar Pranshu, Kuntal Misra, Rithesh A, Jean Surdej, Sarvesh Kumar Yadav

Earth and Planetary Astrophysics · Cross-listed from physics.geo-ph

Mapping deep-mantle compositional heterogeneity using a directional geoneutrino detector

Zhihao Xu, Misaki Hosoya, William F. McDonough et al. (+2 more)

Determining the spatial distribution of heat-producing elements (HPEs) within the Earth is critical for understanding the planet's thermal and chemical evolution. A central debate is whether the deep mantle, particularly the Large Low-Velocity Provinces (LLVPs), retains anomalous, radiogenically enriched reservoirs. While mapping surface variations in geoneutrino flux offers a direct probe of Earth's internal radioactivity, current continental-located detectors measure only the angle-integrated flux. This limitation creates a fundamental parameter degeneracy, rendering it impossible to distinguish a chemically homogeneous mantle from a heterogeneous one. In this study, we quantify the potential of directional geoneutrino detection to overcome this limitation. By evaluating realistic LLVP geometries under the experimental framework of the proposed Ocean Bottom Detector (OBD), we demonstrate that resolving the incoming direction of geoneutrinos can successfully break the non-uniqueness inherent in rate-only measurements. These results indicate that future directional geoneutrino measurements could help determine whether LLVPs host enhanced HPE abundances and assess their contribution to Earth's radiogenic heat budget. Such measurements would provide a new observational constraint on the chemical heterogeneity of the deep mantle and its role in Earth's long-term thermal evolution.
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All authors Zhihao Xu, Misaki Hosoya, William F. McDonough, Taichi Sakai, Hiroko Watanabe

High Energy Astrophysical Phenomena

Gamma-Ray Periodicity in Jetted AGN: Revisiting Periodicity Candidates with >17 years of Fermi-LAT Data

P. Peñil, A. Rico, A. Domínguez et al. (+3 more)

We reanalyze previously reported gamma-ray periodicity candidates in jetted active galactic nuclei using more than 17 years of Fermi-LAT observations. The updated data provide a robust test of whether earlier results correspond to persistent periodic behavior, to transient quasi-periodic oscillations (QPOs), or to fluctuations produced by stochastic variability. We apply complementary timing methods, including the Generalized Lomb-Scargle periodogram, Phase Dispersion Minimization, and Singular Spectrum Analysis, and estimate the test statistics using artificial light curves generated from different variability models, including simple and bending power-law power spectral densities, as well as ARIMA and ARFIMA autoregressive models. We find that most previously proposed candidates in literature are not confirmed when the longer baseline is considered, indicating that many reported periods were likely driven by limited temporal coverage and red-noise variability or transient QPO-like features rather than persistent periodic behavior. Only eight sources retain hints of periodic behavior at the >2sigma local test statistics. Among them, PG 1553+113 and S5 1044+71 remain the most significant cases, with local test statistics above 3sigma, and with a global significance consistent with ~0sigma (because of the large trial factor). In addition, we assess predictions from previous studies as an independent test of the proposed periods and find that some are consistent with the new observations.
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All authors P. Peñil, A. Rico, A. Domínguez, M. Ajello, S. Buson, S. Adhikari

High Energy Astrophysical Phenomena

Mrk 382: A Narrow-line Seyfert 1 Galaxy with Recurrent X-ray State Transitions

Yanli Ai, Wenfeng Wen, Liming Dou et al. (+10 more)

We report recurrent X-ray state transitions in the nearby narrow-line Seyfert~1 galaxy Mrk~382 using multi-epoch observations from Swift, Chandra, XMM-Newton, and eROSITA, together with archival ultraviolet, optical, and infrared data. The 0.3–2 keV flux varies by nearly an order of magnitude over the past $\sim15$ yr, with multiple transitions between bright and faint states. The source brightened by a factor of $\sim10$ between the 2010 Chandra observation and the 2011 XMM-Newton high state, then declined by $\sim6$–7 to a low state in 2019, followed by renewed brightening in recent Swift monitoring. The X-ray spectrum shows strong state-dependent evolution, changing from a steep high-state continuum ($\Gamma=2.32\pm0.04$) to a much harder low-state spectrum ($\Gamma=1.39\pm0.06$). The low-state spectrum also exhibits a narrow Fe K$\alpha$ line with an equivalent width of $\sim330$ eV. Reflection modeling indicates that the low-flux state is strongly reflection dominated, with the reflection fraction increasing from $R_{\rm refl}\sim4$ to $\sim34$, consistent with a compact corona subject to strong light-bending effects. The ultraviolet emission broadly follows the long-term X-ray variability but with smaller amplitude, while the optical and mid-infrared bands vary more mildly. Despite the dramatic X-ray variability, Mrk~382 does not enter an extreme X-ray-weak state, and we did not detect clear optical spectral-type changes based on the currently available observations. Mrk~382 is therefore a rare nearby Seyfert galaxy undergoing recurrent X-ray state transitions, providing a valuable laboratory for studying changing coronal geometry and multiwavelength AGN variability.
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All authors Yanli Ai, Wenfeng Wen, Liming Dou, Jiahua Wu, Chen Hu, Tinggui Wang, Xiaohui Yang, Jing Wang, Xue-Bing Wu, Qiusheng Gu, Xinwen Shu, Pudu, Jian-Min Wang

Solar and Stellar Astrophysics

Photometric and spectral variability of the candidate post-AGB star IRAS 07506-0345

N.P. Ikonnikova, M.A. Burlak and A.V. Dodin

We report photometric and spectroscopic observations of the poorly studied post-AGB candidate IRAS 07506-0345, obtained with the telescopes of the Caucasian Mountain Observatory of SAI MSU in 2023-2026. The star exhibits Cepheid-like variability with a pulsation period of P = 33.68 days. Low-resolution spectra reveal a strong CN molecular band at $\lambda$ 3883, characteristic of carbon-rich post-AGB objects, while H$\alpha$ shows phase-dependent emission and P~Cyg-type profiles, indicating shock waves and mass outflow. Radial velocities are measured from multiple spectral lines. Using period-luminosity-color relations for Type II Cepheids, we estimate a luminosity of $L = 1050\pm250\,L_\odot$. The combined properties - period, amplitude, light-curve morphology, infrared excess, low metallicity, and hydrogen line emissions - securely classify IRAS 07506-0345 as an RV Tau variable.
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High Energy Astrophysical Phenomena

From One to Two: A Second Binary Millisecond Pulsar in the Globular Cluster M92 (NGC 6341)

Dejiang Yin, Li-yun Zhang, Baoda Li et al. (+4 more)

We report the discovery and phase connected-timing solution of a second millisecond binary pulsar, PSR J1717+4308B (M92B), in the globular cluster M92 (NGC 6341) using the Five-hundred-meter Aperture Spherical radio Telescope. This new pulsar, with a spin period of 3.51 ms and a dispersion measure (DM) of 35.29 pc cm$^{-3}$, was discovered through frequency-domain acceleration searches. The timing solution shows that M92B is in a binary system with an orbital period of 2.3 days, an eccentricity of $\simeq 4.8 \times 10^{-4}$, and a minimum companion mass of 0.2 $\,M_\odot$. M92B lies within the cluster core radius in projection, and its negative spin period derivative ($\dot{P}$) is consistent with acceleration in the cluster potential. The measured negative $\dot{P}$ of M92B, together with a DM consistent with that of M92A ($< 0.2\, \rm pc\,cm^{-3}$), confirms that both pulsars are members of the cluster. A Bayesian Markov Chain Monte Carlo analysis based on these two pulsars yields broad constraints on the core structural parameters of M92 that are consistent with $N$-body dynamical modeling. This demonstrates that pulsar timing can provide useful dynamical information in sparse pulsar samples.
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All authors Dejiang Yin, Li-yun Zhang, Baoda Li, Yinfeng Dai, Lin Wang, Qiuyu Yu, Yujie Lian

Instrumentation and Methods for Astrophysics · Cross-listed from cs.CL

LLM Judges Have Dark Current: Stratified Null and Utility Tests for LLM Judge Reliability

Hiroyasu Usami, Keisuke Hara, Ayato Tsuboi et al. (+1 more)

Passing an exact-clone null gate does not entail passing a matched target-selection utility gate. We call a non-tie preference between exact duplicates dark current. On 102 prespecified fresh RewardBench 2 rows, all four configuration–criterion cells report 0/102 clone preferences. Both neutral utility arms pass, but strict utility lower bounds of .539 and .745 miss the .75 working threshold. Conversely, re-evaluation of the same rows on two additional configurations yields a neutral gpt-oss utility pass with 2/102 clone preferences, leaving low-null behavior uncertified. A separately frozen 485-row extension passes both aggregate working gates under both criteria on one local raw-text configuration, yet strict Precise Instruction Following (Precise IF) alignment is 58/154 (.377). Thus matched null and utility results can diverge, and aggregate passage can coexist with weak subset alignment. Interpretation is conditional on the declared configurations, fixed source mixtures, source-label targets, and study-specific working models. The bounds are marginal, the subset rate is descriptive, and non-certification does not prove a defect.
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All authors Hiroyasu Usami, Keisuke Hara, Ayato Tsuboi, Naohiko Matsuda

2606.15610 · 14 Jun · 21 pages, 4 figures, 9 tables. Substantially revised: input-stratified null and target-selection utility audits, additional fixed-configuration studies, and an operational audit protocol. Supersedes v1, originally titled "LLM Judges Have Dark Current: A Psychometric Datasheet for LLM-as-a-Judge Evaluation."

Abstract PDF $ALIGN ×2$CELL ×1

Cosmology and Nongalactic Astrophysics

Impact of CMB low-$\ell$ EE polarization data on dark energy parameterizations

Shubham Barua and Shantanu Desai

Measurement of the optical depth to reionization ($\tau_\mathrm{reio}$) is largely driven by the large-scale EE polarization data of CMB ($\ell<30$). Removing the low-$\ell$ EE data potentially alleviates various cosmological tensions. In this work, we study the effect of the low-$\ell$ EE polarization measurements on the CPL, JBP and BA dark energy parameterizations using CMB data from Planck and ACT DR6, combined with DESI BAO and PantheonPlus compilation of Type Ia supernovae. We find that excluding low-$\ell$ EE data shifts $\tau_\mathrm{reio}$ and $A_s$ to higher values through the unbroken $A_s-\tau_\mathrm{reio}$ degeneracy with a $\sim(1.4-1.8)\sigma$ shift in $A_s$ for $\Lambda$CDM and JBP, and a milder $\sim 1\sigma$ shift for CPL and BA. The equation of state (EOS) for all three parameterizations moves towards the quintessence regime ($w(z) > -1$) upon exclusion of low-$\ell$ EE data, driven primarily by the strengthening of the $w_a-A_s$ and the $w_a-\tau_\mathrm{reio}$ correlations, with a small effect from the correlations of $w_0$ with $A_s$ and $\tau_\mathrm{reio}$. The most prominent effect occurs in JBP, where the EOS lies entirely within the quintessence regime at $1\sigma$ when excluding low-$\ell$ EE data. Model comparison through AIC shows positive evidence in favor of CPL and BA and weak evidence in favor of JBP, robust to the inclusion of low-$\ell$ EE data and CMB data used. DIC model comparison shows strong evidence in favor of CPL and BA when low-$\ell$ EE data is included, and positive evidence when it is excluded. For JBP, we get positive (weak) evidence when including (excluding) low-$\ell$ EE data over $\Lambda$CDM.
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Saturday 13 June

Instrumentation and Methods for Astrophysics · Cross-listed from cs.DC

Is RISC-V Ready for Massively Parallel Astrophysical Codes?

Jenny Lynn Almerol, Nitin Shukla, Federico Ficarelli et al. (+5 more)

We present a performance and portability evaluation of three well-established astrophysical production codes, namely iPIC3D, PLUTO, and OpenGadget3, on a Sophgo SG2044 RISC-V processor (part of the Monte Cimone cluster), with comparisons to AMD EPYC 9554 (x86) and NVIDIA GH200 Grace (ARM) systems. These applications represent memory-bound, compute-bound, and hybrid workloads, respectively. Numerical correctness is verified across all platforms, confirming portability. RISC-V shows consistently lower performance, with slowdowns of about $3-6\times$ relative to x86 and $5-9\times$ relative to ARM. The gap is mainly due to limited memory bandwidth, shared cache constraints, narrower 128-bit vector units, and lower clock frequency, but also less-mature auto-vectorization capability of the GNU compiler suite. Memory-bound kernels are the most affected, where early bandwidth saturation and L2 cache contention reduce scalability at higher thread counts. Hybrid MPI+OpenMP configurations reveal a trade-off between memory contention and communication overhead, with intermediate configurations achieving the best performance. These results suggest that RISC-V is capable of supporting scientific workloads; however, additional improvements in both hardware and compiler technology, particularly in auto-vectorization, are required to achieve competitive performance.
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All authors Jenny Lynn Almerol, Nitin Shukla, Federico Ficarelli, Geray S. Karademir, Andrea Bartolini, Emanuele Venieri, Giacomo Madella, Elisabetta Boella

Earth and Planetary Astrophysics

Low-spin ferrous iron suppresses mantle oxidation beyond Earth-like pressures

Alice Girani, Sylvain Petitgirard, Sergey Yaroslavstsev et al. (+5 more)

The Earth's mantle has elevated Fe$^{3+}$ relative to those of other rocky bodies, yet the oxidation- and electronic state of iron at extreme pressures is poorly known. We present in-situ energy-domain synchrotron Mössbauer spectra of $^{57}$Fe-enriched silicate glasses at 298 K from 1 bar to 174 GPa in a diamond anvil cell. Glasses were synthesised with Fe$^{3+}$/[Fe$^{3+}$ + Fe$^{2+}$] from 0.02 $\pm$ 0.02 to 1.00 $\pm$ 0.02, as determined by colourimetry. While pure Fe$^{3+}$-basaltic glass shows minimal changes up to 174 GPa, the spectra of Fe$^{2+}$-peridotitic and basaltic glasses are fit by two doublets, D$_1$ and D$_2$. At 1 bar, their relative intensities are $\sim$92 % and $\sim$8 %, respectively, but the integral area ratio, D$_2$/(D$_1$ + D$_2$), reaches 0.65 by 172 GPa. Because this transition is reversible with pressure and no metallic iron is detected, the D$_2$ feature is Fe$^{2+}$ low spin (LS), whereas D$_1$ is Fe$^{2+}$ high spin (HS). Consequently, the Fe$^{3+}$/[Fe$^{3+}$+Fe$^{2+}$] of planetary mantles reach a maximum near $\sim$40 GPa, before decreasing at higher pressures due to the stabilisation of Fe$^{2+}_{\mathrm{{LS}}}$. This peak coincides with estimated core-mantle equilibrium on Earth, implying that its uniquely oxidised mantle and habitable state may result from core formation within a Goldilocks pressure range. Secondary atmospheres are predicted to transition from H$_2$-rich for Moon-sized bodies, to CO-rich for Earth-like planets and H$_2$- and CH$_4$-bearing around super-Earths and sub-Neptunes.
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All authors Alice Girani, Sylvain Petitgirard, Sergey Yaroslavstsev, Georgios Aprilis, James Badro, Antoine Bézos, Hugh St.C. O'Neill, Paolo A. Sossi